A torque tube transmits static and dynamic torsional loads in power transmission applications. For example, torque tubes are commonly used in aircraft to provide power transmission for actuating and braking flight control surfaces, e.g. flaps and slats, and for actuating aircraft doors and door latches. Each end of a torque tube may be provided with a coupling feature configured for mechanically coupling the torque tube to another transmission mechanism in the drive line. For example, one or both ends of a torque tube may include a flange having an array or pattern of bolt holes used for coupling.
So-called “composite” torque tubes made by helically winding or wrapping carbon fiber tow around a cylindrical mandrel are widely used in the aircraft industry in part because they are lighter than metal torque tubes yet still meet critical strength requirements. Composite torque tubes also offer improved flexural rigidity and torsional rigidity. However, because the coupling features at the ends of the torque tube differ from and are more complex than the straight length of the torque tube between the ends, the coupling features are not formed of wrapped composite material. Instead, it is known to manufacture a metallic end fitting that includes the coupling feature, and form the torque tube as a hybrid assembly having a pair of metal end fittings connected by a straight tube of wrapped composite material. In this regard, see U.S. Pat. No. 7,335,108 (Lin et al.); U.S. Pat. No. 7,419,435 (Borges et al.); U.S. Pat. No. 7,682,256 (Brace et al.); U.S. Pat. No. 7,874,925 (Dewhirst); and U.S. Pat. No. 8,025,580 (Genot et al.). The metal end fittings add weight, and it is a challenge to ensure that the junction between the composite material and each metal end fitting is reliable and not prone to failure under loading.
U.S. Pat. No. 3,651,661 (Darrow), teaches making a composite torque tube having typical bolt-hole flanges by laying alternating plies of composite fabric on a cylindrical mandrel. The flanges are made by folding out fingers or strips provided in the fabric plies. This patent does not teach winding fiber tow.
U.S. Pat. No. 5,397,272 (Smiley et al.) describes an all-composite torque tube that teaches wrapping fiber around an arbor and integrally forming two yoke lugs of a universal joint at an end of the tube. The lugs extend parallel to one another in an axial direction of the torque tube and include respective holes aligned with one another along a diametric axis for receiving a coupling member of the universal joint.
Outside the torque tube art, U.S. Pat. No. 8,118,958 (Lunin et al.) teaches a method for manufacturing an output arm for a rotary actuator by winding a composite fiber filament about a pair of metal eyelets and a metal gear insert. The eyelets and gear insert are supported on a fixture during winding. The wound filament is then infused with resin and the resin is cured. The fixture is removed to yield a finished actuator arm.
A need remains for an all-composite torque tube having flanges with bolt holes at its opposite ends, wherein the torque tube is economical to manufacture and does not require metal end fittings.